Method for increasing the manoeuvrability or driving stability of a vehicle during cornering

ABSTRACT

In a method for increasing the maneuverability and driving stability of an automotive vehicle during cornering, the rotational behavior or the wheel slip of the individual vehicle wheels is monitored, and the distribution of the brake force to the curve-outward wheels compared to the brake force conducted to the curve-inward wheels is varied in dependence on the wheel rotational behavior and/or the slip of the wheels. When cornering is detected, a total deceleration of the vehicle that corresponds to the driver&#39;s request is determined, and a vehicle deceleration that corresponds to the driver&#39;s request is achieved by increasing the brake force (ΔP 1 ) at the curve-outward wheel(s) and decreasing or maintaining the brake force at the curve-inward wheels.

[0001] The present invention relates to a method for increasing themaneuverability and/or driving stability of an automotive vehicleequipped with a controlled brake system, wherein the rotational behaviorand/or the wheel slip of the individual vehicle wheels during corneringis monitored, and wherein when cornering is detected, the distributionof the brake force to the curve-outward wheels and the curve-inwardwheels is varied in dependence on the wheel rotational behavior and/orthe wheel slip. A brake system for implementing the present method isalso covered by the present invention.

[0002] DE 195 22 632 A1 discloses a method of this type wherein aswitch-over from a normal control mode to a cornering control mode iseffected when cornering is detected in order to improve the steerabilityof the vehicle and its driving stability. In this special mode, comparedto the normal control mode, the mean pressure level of the curve-inwardfront wheel is decreased by a predetermined value and the mean pressurelevel of the curve-outward front wheel is raised by a predeterminedvalue. This method concerns improving the control behavior of ananti-lock control system (ABS) during cornering, for what reason theterm ABSplus (improved ABS) or ESBS (Enhanced Stability Brake System) isused. Brake pressure increase (at the curve-outward front wheel) inexcess of the pilot pressure produced by brake pedal application isneither arranged for, nor possible.

[0003] Further, it is known from DE 196 48 909 A1 with a view toimproving the control behavior of an anti-lock brake system which is aptfor active braking intervention to initiate a special control if, duringcornering without brake application, a deceleration of the vehicle isdetected and if, simultaneously, a critical wheel slip conditionindicative of inward steering of the vehicle (oversteering) issatisfied, the said special control effecting the introduction of brakepressure into the wheel brake of the curve-outward front wheel. Thisspecial control which prevents oversteering of the vehicle is infunction only when the brake is not applied.

[0004] An object of the present invention is to improve upon a method ora brake system of the type mentioned hereinabove to such effect thatwhen traveling in a curve, when changing lanes, or in similar maneuvers,a good steerability and high driving stability as well as a shortstopping distance or a precise brake effect is achieved which lattercorresponds to the driver's request that is expressed by the extent ofbrake pedal application. The objective is to convert the driver'srequest into a corresponding vehicle deceleration both in emergencybrake situations and in the event of a ‘gentle’ pedal application.

[0005] It has proved that this object may be achieved by the method asdescribed in claim 1, the special characteristics of which includes thatduring cornering detection, a total deceleration of the vehicle whichcorresponds to the driver's request is determined, and that the vehicledeceleration which corresponds to the pedal force or the driver'srequest is achieved by increasing the brake force at the curve-outwardfront wheel and/or rear wheel in excess of the brake force thatcorresponds to the driver's request and by decreasing the brake force ormaintaining the brake force constant at the curve-inward wheel(s).

[0006] According to the present invention, the brake pressure and,hence, the brake force is increased at the curve-outward front wheel,yet decreased or maintained constant at the curve-inward front wheel forcompensating an oversteering driving behavior which may e.g. occurduring cornering, in the event of a sudden change of lanes, etc. Theunsymmetric distribution of the brake forces on the front axle isadapted to driving conditions by the control system.

[0007] In conventional systems with an improved steerability byvariation of the pressure level at the curve-outward and curve-inwardwheel, the (increased) brake pressure at the curve-outward wheel is notable or allowed (the brake system is so designed) to exceed the pilotpressure predetermined by the pedal application or the brake forcepredetermined by the pedal force. Consequently, the total decelerationof the vehicle compared to straight travel or a cornering maneuver withlike brake pressures at the curve-outward and curve-inward wheelsautomatically becomes lower. This is confusing at least for the driverand demands an adaption to the special situation. The method of thepresent invention, however, permits achieving the total decelerationdesired by the driver even during cornering, in the event of a suddenchange of lanes, etc.

[0008] It is favorable to build up pressure at the curve-outward wheelbeyond the driver's specification as a consequence of the method of thepresent invention also with low pressure specifications set by thedriver, where it would be impossible to generate the necessarystabilizing moment by a pressure buildup (at the curve-inward wheel)alone.

[0009] In advantageous alternative embodiments of the method of thepresent invention, the increase of the brake force at the curve-outwardwheels and the decrease at the curve-inward wheels may be effectedsimultaneously or within a predetermined period in steps, e.g. bypressure variation pulses or pressure variation pulse trains. On theother hand, it is also possible and even favorable in many cases toperform the increase at the curve-outward wheels and the correspondingdecrease at the curve-inward wheels in a deferred manner. In thisarrangement, the increase of the brake force e.g. by a predeterminedperiod in the magnitude of 50 ms to 500 ms should be carried outsubsequent to the brake force decrease at the curve-inward wheel or thecurve-inward wheels.

[0010] A brake system which is especially appropriate for implementingthe method of the present invention is configured as a so-calledbrake-by-wire system (BBW), e.g. as an electrohydraulic brake system(EHB) or electromechanic brake system (EMB). In brake systems of thistype, the pedal application or the driver's request expressed by pedalapplication is principally sensed and transmitted in the form of anelectric signal to the brake force generating means. It is not difficultin such systems to achieve a brake force increase at the curve-outwardwheel beyond the driver's request.

[0011] Further favorable embodiments of the method of the presentinvention and of brake systems for implementing the method are describedin the accompanying subclaims.

[0012] Further advantages, features, and possible applications of thepresent invention can be taken from the following description of detailsand embodiments by way of the attached drawings.

[0013] In the drawings,

[0014]FIG. 1 is a schematically simplified view of a brake system forimplementing the method of the present invention.

[0015]FIG. 2 is a schematically simplified view of components of a brakesystem of the present invention.

[0016]FIG. 3 is another embodiment of a brake system of the presentinvention.

[0017]FIG. 4 is a diagram showing the variation of the brake pressuredifference at the curve-inward and curve-outward front wheel accordingto an embodiment of the present invention.

[0018] According to the principle of the present invention illustratedby way of FIG. 1, the ‘driver's request’ which is expressed byapplication of the brake pedal is initially realized by a block 1referred to as EBD (Electronic Brake Force Distribution) is realized inbrake force components or pressure components P₁ to P₄ for theindividual vehicle wheels 1 to 4. In a subsequent block or a processingstep 2 which is called by experts ‘ESBS pressure distribution’ (brakesystems of this type are referred to as ‘ABSplus’ systems or ‘EnhancedStability Brake Systems’) in FIG. 1, the pressure or brake forcecomponents P₁ to P₄ associated with the individual wheels duringcornering detection (FKE) are modified according to the specificationsof the method of the present invention so that pressure or brake forcecomponents P₁′ to P₄′ are available at the output of step 2.

[0019] Cornering detection may be realized in very different fashions.E.g. cornering detection by monitoring the slip variations of theindividual wheels is known in the art. At least seemingly, there is adifferent slip at the curve-outward wheels compared to the curve-inwardvehicle wheels.

[0020] An oversteering vehicle is illustrated symbolically in the bottompart of FIG. 1 to make clear that in the event of implementation of themethod of this invention, the pressure (or the brake force) P₁calculated in step 1 is increased by a defined amount ΔP₁ at thecurve-outward front wheel V_(outw.), while the pressure P₂ at thecurve-inward front wheel V_(inw.) is lowered by a differential pressureΔP₂. Consequently, the brake pressure P₁′ is higher than the brakepressure P₁ which corresponds to the driver's request. This is ofdecisive importance to the present invention.

[0021] As another embodiment of the present invention, FIG. 2schematically shows a brake system wherein the pedal force or thepressure ‘P_(stat.)1 . . . 4’ which expresses the ‘driver's request’ andapplies in the static condition of the vehicle and during straighttravel, is sent to a brake force distributor 3 (EBD), on the one hand,and, on the other hand, to a step 4 referred to as ‘ESBS’ in which thespecial conditions during cornering maneuvers are taken into account.The dynamic components ‘P_(dyn) (EBD)1 . . . 4’ calculated by theelectronic brake force distribution EBD 3 and the dynamic componentsP_(dyn) (ESBS)1 . . . 4 responsive to cornering are evaluated in adistribution step 5, referred to as ‘pressure arbitration’, with a viewto calculating the components ‘P_(dyn)1 . . . 4’ sent to the individualvehicle wheels.

[0022] In FIG. 3 another embodiment of a brake system for implementingthe method of the present invention is shown. The ‘detection of thedriver's request’ is represented by block 6 having an output signalwhich is sent to an electronic brake force distribution 7 that takes thestatic conditions into account. An arithmetic unit 8 which represents anadaption algorithm for the adaptive portion of the brake forcedistribution under static conditions is used for detecting the drivingsituation (cornering or straight travel, rough roads, etc.), forprocessing the speeds V₁ to V₄ of the individual vehicle wheels and forevaluating these input quantities.

[0023] The output information or signals of the static brake forcedistribution 7, i.e., the individual components ‘P1stat’ to ‘P4stat’ areevaluated in a block 9 in which the dynamic components ‘P1dyn’ to‘P4dyn’ of the brake force distribution are calculated on the basis ofthe static components ‘P1stat’ to ‘P4stat’ and the wheel speeds V₁ to 4.

[0024]FIG. 3 represents the brake force distribution concept of abrake-by-wire system, especially of an electrohydraulic brake system(EHD) wherein the present invention is implemented.

[0025]FIG. 4 still shows a diagram for illustrating another embodimentof the present invention which includes that the pressure differentialcomponents for considering a cornering maneuver, i.e., the pressurecompensation components ΔP₁, −ΔP₂ (see FIG. 1) are added to the wheelbrake pressure P₁, P₂ (see FIG. 1) deferred in time in order to ensure acomfortable generation of the necessary yaw torque for assisting thecornering maneuver. Pressure correction starts at time t₀. In theillustrated embodiment, the wheel brake pressure at the curve-inwardfront wheel is initially lowered by roughly 5 bar (corresponds to ΔP₂ inFIG. 1), and only subsequent thereto, in this case after 200 ms at timet₁, will the wheel brake pressure at the curve-outward front wheel beincreased by likewise 5 bar (ΔP₁). This is repeated after a pause of 1second approximately. In practice, these brake force or pressurevariations are realized by pulse trains, such as in the embodiment ofFIG. 4, or by exactly calculated individual pulses. The duration of thepressure variation pulses can range from 50 ms to some 100 ms.

[0026] In other cases, however, a simultaneous brake force or brakepressure increase at the respective front wheels caused by individualpulses or pulse trains is assumed to be sufficient.

1. Method for increasing the maneuverability and/or driving stability ofan automotive vehicle equipped with a controlled brake system, whereinthe rotational behavior and/or the wheel slip of the individual vehiclewheels during cornering is monitored, and wherein when cornering isdetected, the distribution of the brake force to the curve-outwardwheels and the curve-inward wheels is varied in dependence on the wheelrotational behavior and/or the wheel slip, characterized in that duringcornering detection, a deceleration of the vehicle which corresponds tothe driver's request is determined, and in that the vehicle decelerationwhich corresponds to the driver's request is achieved by increasing thebrake force at the curve-outward front wheel and/or the curve-outwardrear wheel in excess of the brake force that corresponds to the driver'srequest and by decreasing the brake force at the curve-inward wheel(s).2. Method as claimed in claim 1, characterized in that the brake forceis increased at the curve-outward wheels and decreased at thecurve-inward wheels simultaneously or within a predetermined time periodin steps, e.g. by pressure variation pulses or pulse trains.
 3. Methodas claimed in claim 1, characterized in that the increase of the brakeforce at the curve-outward wheels and the decrease thereof at thecurve-inward wheels is effected in a deferred manner, e.g. offset by aperiod of time in the magnitude of 50 ms to 500 ms, especially 200 ms.4. Method as claimed in claim 3, characterized in that the increase inthe brake force at the curve-outward wheels is initiated subsequent tothe decrease of the brake force at the curve-inward wheels or followingthe corresponding decrease pulse.
 5. Method as claimed in any one ormore of claims 1 to 4, characterized in that several consecutive actionsof brake force increase and brake force decrease are performed inpredetermined time intervals of e.g. 1 to 2 sec.
 6. Brake system forimplementing the method as claimed in any one or more of claims 1 to 5,characterized in that the said brake system is configured as a‘brake-by-wire system’, e.g. as an electrohydraulic brake system (EHB)or an electromechanic brake system (EMB).
 7. Brake system as claimed inclaim 6, characterized in that the said system comprises an EBD control(Electronic Brake Force Distribution), wherein the static distributionof the brake pressures to front axle and rear axle of the automotivevehicle is defined by characteristic curves (FIG. 2, FIG. 3).
 8. Brakesystem as claimed in claim 6 or 7, characterized in that for theadaption of the brake force distribution (EBD), the staticcharacteristic curves of the brake force distribution are adapted to theload condition of the vehicle and the condition of the brake system by asuperposed algorithm, and the adaption is effected by evaluating theinformation about wheel rotational speeds and internal controlconditions.
 9. Brake system as claimed in any one or more of claims 6 to8, characterized in that additional sensor means provided in the vehiclesuch as steering angle sensor, transverse acceleration sensor,longitudinal acceleration sensor, and yaw rate sensor are evaluated toimprove and secure the input data of the brake system.
 10. Brake systemas claimed in any one or more of claims 6 to 9, characterized in thatthere is an EBD control step which calculates the distribution of thebrake pressures of all wheels, which is optimal in the current drivingsituation, based on the static specification of the brake pressures andthe behavior of the vehicle during cornering.
 11. Brake system asclaimed in claim 10, characterized in that the EBD control step isdesigned so that the resulting total deceleration of the vehiclecorresponds to the driver's request also during the EBD function.